1. Field
The present invention relates to the recovery of metal values from aqueous systems by extraction with an organic solvent or resin having minimal aqueous solubility.
2. Prior Art
Extraction of metal values from aqueous systems by means of ion exchange techniques such as solvent extraction has achieved prominence in hydrometallurgical processing technology.
Ion exchange and solvent extraction are widely used in hydrometallurgy and water purification. Solvent extraction, which is carried out by various organic liquid extractants, with or without diluents or modifiers, has been used in hydrometallurgy for the recovery of uranium, copper, and other metals. Synthetic resins which contain functional groups similar to those used in solvent extraction are also widely used for waste water purification and in hydrometallurgy for the separation of metallic ions. The use of resins with active functional groups is a form of extraction that involves a solid substrate. Such a substrate may be, but need not be, active in the ion extraction process. It may function merely as a carrier for an active extractant.
Recovery of metal values from aqueous systems by organic acids, amines, phosphorus oxide compounds and the like is frequently accomplished from acidic systems. Such extraction is conducted in systems having a pH of less than 7.
Solvent extraction of gold has not been practiced heretofore in industry. Laboratory experiments reported in the literature indicate that the extraction of gold from cyanide solutions is possible with weak base amines and neutral extractants such as long chain alcohols, ketones, and the like under acidic conditions.
Extraction of metal values from cyanide systems is generally not practiced industrially inasmuch as cyanide gas may evolve at low pH conditions in which solvent extraction procedures employing amines and the like have been practiced.